We are using psychophysical and electrophysiological measures to determine the origin of the effects of acute and chronic methadone on visual reaction time performance in addicts and non-addicts. While addicts are faster than non-addicts in such tests, the performance of non-addicts slows in a dose-related fashion with acute methadone . The slowing of visual reaction time with acute methadone in non-addicts is not related to attentional or motivational decrements. Group differences in reaction time cannot be explained by these factors either. Detection performance of non-addict controls on a two flash visual detection test performed within a Theory of Signal Detectability framework decreases with increasing dose of methadone and has a time course of effect parallel to subjective effects of the drug. Potentials recorded from scalp occipital leads evoked by the onsets of each of the flashes also show drug related changes, which largely drop out as performance returns to normal after drug. Preliminary data indicate that "class 2" units (with presumed origin in ganglion cells of retina) recorded by extracellular electrodes in tectum of frog show decreased responsiveness to visual stimuli after IP methadone. Drop in responsiveness can be reversed by administration of a narcotic blocking agent, Naloxone. We are starting data collection on the auditory and visual reaction time performance of addicts and non-addicts to determine the role of input modality on the previously reported visual reaction time differences between the groups. All of the research is directed toward exploring the effects of acute and chronic methadone on visual function. BIBLIOGRAPHIC REFERENCES: S. Rothenberg, S. Schottenfeld, R.E. Meyer, B. Krauss, and K. Gross. Performance differences between addicts and non-addicts. Psychopharmacology (in press) 1977.